# Concurrency, retrieval exception

**URL:** https://discuss.dgraph.io/t/concurrency-retrieval-exception/12117
**Category:** Dgraph
**Tags:** kind:question, dgraph
**Created:** [December 30, 2020, 3:12am UTC](https://discuss.dgraph.io/t/concurrency-retrieval-exception/12117 "2020-12-30T03:12:26Z")
**Posts on this page:** 5
**Page:** 1

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### Author: ![musiciansLyf](https://yyz1.discourse-cdn.com/flex007/user_avatar/discuss.dgraph.io/musicianslyf/32/5834_2.png) [@musiciansLyf](https://discuss.dgraph.io/u/musiciansLyf)
#### Post date: [December 30, 2020, 3:12am UTC](https://discuss.dgraph.io/t/concurrency-retrieval-exception/12117/1 "2020-12-30T03:12:26Z")

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Hello, excuse me. I have two questions

1: There are 50 concurrent threads. After a thread submits a mutation transaction and creates a node, other threads immediately retrieve it. Some of them return empty, and some of them can retrieve it. As a result, multiple nodes are created. What if this situation is avoided?

2: After 7000 nodes in 20.03.0, if the three EQ continuous and retrieval data is empty, a single EQ can retrieve the node, and the node does meet the conditions. Is there any restriction on the index file?

Please take a look, thank you!

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### Author: ![chewxy](https://yyz1.discourse-cdn.com/flex007/user_avatar/discuss.dgraph.io/chewxy/32/4339_2.png) [@chewxy](https://discuss.dgraph.io/u/chewxy)
#### Post date: [December 30, 2020, 3:42am UTC](https://discuss.dgraph.io/t/concurrency-retrieval-exception/12117/2 "2020-12-30T03:42:46Z")

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I am struggling a bit to understand the problem. What is EQ?

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### Author: ![musiciansLyf](https://yyz1.discourse-cdn.com/flex007/user_avatar/discuss.dgraph.io/musicianslyf/32/5834_2.png) [@musiciansLyf](https://discuss.dgraph.io/u/musiciansLyf)
#### Post date: [December 30, 2020, 5:00am UTC](https://discuss.dgraph.io/t/concurrency-retrieval-exception/12117/3 "2020-12-30T05:00:46Z")

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like this

 ![image](https://canada1.discourse-cdn.com/flex007/uploads/dgraph/original/2X/4/4ffddbd7d2752f964f77ba8dd43b20d55b0bab33.jpeg)

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### Author: ![musiciansLyf](https://yyz1.discourse-cdn.com/flex007/user_avatar/discuss.dgraph.io/musicianslyf/32/5834_2.png) [@musiciansLyf](https://discuss.dgraph.io/u/musiciansLyf)
#### Post date: [December 30, 2020, 5:01am UTC](https://discuss.dgraph.io/t/concurrency-retrieval-exception/12117/4 "2020-12-30T05:01:24Z")

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And this is what we can retrieve

 ![image](https://canada1.discourse-cdn.com/flex007/uploads/dgraph/original/2X/8/83dd5bb55567fd77124b239383839990cf5ba9e1.jpeg)

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<div class="post-metadata">

### Author: ![musiciansLyf](https://yyz1.discourse-cdn.com/flex007/user_avatar/discuss.dgraph.io/musicianslyf/32/5834_2.png) [@musiciansLyf](https://discuss.dgraph.io/u/musiciansLyf)
#### Post date: [December 31, 2020, 6:15am UTC](https://discuss.dgraph.io/t/concurrency-retrieval-exception/12117/5 "2020-12-31T06:15:59Z")

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There is no recurrence of the above problem in v20.11.0. The previous version was v20.03.0. Is it fixed? Or is the number of nodes not up to the limit? At present, it is 50000 nodes.